1. Field of the Invention
The present invention relates to an actuator used for a liquid discharge head mounted on a liquid discharge recording apparatus, as well as to a liquid discharge head. The invention also relates to a method for manufacturing a liquid discharge head.
2. Related Background Art
In recent years, the printer that adopts a liquid discharge recording apparatus as the printing apparatus for a personal computer and the like has been widely used for the reasons that it has an excellent printing performance with easier handling at lower costs, among some others. For the liquid discharge recording apparatuses of the kind, there are those adopting various methods; the one that discharges liquid droplets by means of the pressure wave of the bubble, which is generated by bubbling in liquid, such as ink, by the application of thermal energy; the one that enables liquid droplets to be sucked and discharged by means of electrostatic force; and the one that utilizes the pressure wave generated by a vibrator, such as piezoelectric element, and some others. Generally, the one that uses piezoelectric element is structured with a pressure chamber communicated with a liquid supply chamber, and a liquid discharge port communicated with the pressure chamber, for example, and there is provided a vibration plate having piezoelectric element connected with the pressure chamber. Then, with the structure thus formed, the piezoelectric element is stretched and constricted by the application of a specific voltage to the piezoelectric element so as to generate straining vibrations for compressing liquid, such as ink, in the pressure chamber, thus discharging liquid droplets form the liquid discharge ports.
In recent years, color liquid discharge apparatuses have been in wide use, and along with this, it has been required to enhance the printing performance, such as higher resolution, and higher printing speed, in particular. Further, it is required to implement the elongation of liquid discharge head, necessitating the materialization of a multiple-nozzle head structure, which is a more precisely structured liquid discharge head. Then, there is a need for miniaturizing an actuator for discharging liquid in order to make the liquid discharge head more precisely. For the miniaturization of piezoelectric element and/or electrostrictive element (hereinafter referred to as a piezo-electrostrictive element), which constitutes the actuator of the liquid discharge head, it is necessary for the piezoelectric element itself to be made smaller, and then, to be provided with a high piezoelectric constant so as not to allow the driving performance thereof to be lowered even if the element is made smaller.
It is then necessary for the piezoelectric and/or electrostrictive film (hereinafter referred to as an piezo-electrostrictive film) whereby to form the piezoelectric element to be a film having an excellent crystallinity. The film that has the excellent crystallinity is a thin film of the single-orientated crystal, which is orientated in one and the same direction or the monocrystal having in-plane orientation. Also, to make the piezo-electrostrictive film of monocrystal, it is desirable that the immediate layer is monocrystal or the like when manufacturing the piezo-electrostrictive film, and the combination of the piezo-electrostrictive film and the material of the immediate layer should be given an excellent lattice matching.
However, for the piezo-electrostrictive film used for the conventional piezo-electrostrictive element, it is difficult to form the piezo-electrostrictive film thinner than 10 μm, for example, because the adopted method of the film formation is such that the powered paste of PbO, ZrO2, and TiO2 is processed to be a sheet (green sheet) by molding, and after that, the sheet is sintered for the film formation. Also, the sintering of the green sheet is performed at a temperature of 1,000° C. or more. As a result, a problem is encountered that the piezo-electrostrictive material is contracted almost to 70% unavoidably. Under such circumstances, it is difficult to position the piezo-electrostrictive element and the structures, such as the liquid chamber and the pressure chamber, together in a high precision of several-micron order. It is, therefore, difficult to miniaturize the actuator.
Also, the ceramics piezo-electrostrictive film, which is formed by sintering the green sheet, the influence of the grain boundary becomes no longer negligible as the thickness thereof is made smaller. It is then difficult to obtain any good piezo-electrostrictive property. In other words, for the piezo-electrostrictive film obtained by sintering the green sheet, there is a problem that it is difficult to obtain any sufficient piezo-electrostrictive property for discharging recording liquid if the thickness thereof becomes less than 10 μm. Under the circumstances, it has been difficult to materialize a small liquid discharge head having the characteristics needed for discharging recording liquid sufficiently.
Also, as the method of manufacture of the piezo-electrostrictive film, which has been reported up to the present, there are CVD method, Sol-Gel method, and others. The density of piezo-electrostrictive film manufactured by these methods also tends to be lowered to make the micro processing thereof difficult. The piezoelectric constant that indicates the capability of the piezo-electrostrictive material is small, too. Therefore, the displacement amount becomes small against a constant voltage accordingly when it is miniaturized. Thus, it is difficult to adopt the aforesaid CVD method and the like for manufacturing a small actuator and the piezo-electrostrictive film for a liquid discharge head.
Further, with respect to the conventional art, a problem is encountered that the adherence is made lower between metallic electrodes and the piezo-electrostrictive element, which is oxide. There is a need for the provision of high adherence between the electrodes and piezo-electrostrictive film in order to withstand the stress that occurs by the repeated driving when acting as an actuator and piezo-electrostrictive element for a liquid discharge head.
Also, the structure of a liquid discharge head manufactured by the micro processing of semiconductor process using sputtering method, and the method of manufacture therefor have been proposed in the specification of Japanese Patent Application Laid-Open No. 11-348285. This liquid discharge head is characterized in that on the mono-crystal MgO, platinum is orientated for the film formation, and further, thereon, the perovskite layer that does not contain Zr layer, and the PZT layer are formed as a laminated element.
However, with the method of manufacture disclosed in the specification of the aforesaid laid-open paten application, it is difficult to obtain the single-orientated crystal, which is stabilized with good reproducibility or monocrystal PZT. Further, it is impossible to obtain the PZT layer unless it is orientated on an extremely expensive monocrystal substrate, such as monocrystal MgO. The process becomes extremely expensive unavoidably. Further, there is a limit to the size of the MgO mono-crystal substrate to make it difficult to obtain the substrate having a large area.
In this respect, as the oxide electrode material, there is a disclosure of the element that uses SrRuO3 in the specification of Japanese Patent Application Laid-Open No. 06-280023. However, in this specification of patent application, there is no disclosure that SrRuO3 is a crystal having single-orientation or monocrystal, and the thin oxide piezo-electrostrictive film, which should be formed on the upper part, cannot become a crystal having single-orientation or a monocrystal.